1. FIELD OF THE INVENTION
This invention relates to devices for measuring the absorbency of infrared light by hydrocarbon fuels, and more particularly to means and methods of determining the energy content of such fuels from said absorbency.
2. PRIOR ART
Identifying petroleum by infrared absorption "signatures" is disclosed in U.S. Pat. No. 3,896,312, issued July 22, 1975 to Brown et al. Saunders in U.S. Pat No. 3,462,596, issued Aug. 19, 1969, discloses the use of an infrared source to determine the water content of fuel oils. Saunders draws a fuel sample from a supply line and the sample is confined in a low pressure zone in which the water content of the sample fuel oil is flash vaporized. The water vapor is then drawn across a beam of periodically interrupted infrared radiation containing wavelengths of radiation at which water vapor characteristically absorbs. Sarkis in U.S. Pat. No. 3,526,127 issued Sept. 1, 1970, provides a cell through which engine oil samples are passed and subjected to a broad spectrum of infrared light. A standard infrared spectrophotometer records the output. The output is passed to a comparator which compares the infrared characteristics of the oil to evaluation criteria stored in a computer. Heigel in U.S. Pat. No. 2,423,774, issued July 8, 1947, shows a system for comparing the concentration of oil in an oil well sample to a reference sample. Heigel extracts oil from the oil well sample by use of a solvent, then passes light of various wavelengths through the reference sample as well as the oil well-solvent sample. Dille in U.S. Pat. No. 4,045,671, issued Aug. 30, 1977 uses a solvent to extract oil from water and then subjects the oil-solvent sample to infrared light to thereby determine the oil content of the sample from the absorbency of the infrared light by the oil sample.
Systems where frustrated total internal reflection is employed to measure the absorbence of infrared light in materials are generally known. For example, Wilks in U.S. Pat. No. 3,370,502, issued Feb. 27, 1968, discloses a general system for identifying materials wherein a rod transparent to light wavelengths of interest, including possibly infrared light, is placed in a chamber. The material to be identified is placed in the chamber in contact with the rod and light is transmittted by total internal reflection down the rod with energy from the light beam being "diffused from" the rod "according to the material" surrounding the chamber. Harrick in U.S. Pat. No. 3,431,411 inserts a light pipe in powered solid samples and measures the amount of infrared light absorbed by the powered sample as infrared light is totally internally reflected along the light pipe. A similar system is disclosed by Sanden in U.S. Pat. No. 4,228,192, issued Oct. 14, 1980, to quantatively determine the ingredients in beer.
Not disclosed in the prior art, however, are infrared spectrographic means or methods of determining the energy content of a hydrocarbon fuel or the rate of fuel energy consumption. Such means or methods can be useful in gas furnace control, airplane turbine control or in systems for monitoring fuel quality. Improvements in engine performance and fuel efficiency can be realized with such means and methods since critical operating parameters dependent on energy content can be precisely controlled.